The present invention relates to a method and apparatus for producing clean dry air in which compressed air is fed to an adsorption bed system to remove impurities such as moisture and carbon dioxide. More particularly, the present invention relates to such a method and apparatus in which the feed air, after having been purified in the adsorption bed system, is introduced into a catalytic reactor to react hydrocarbons, carbon monoxide and hydrogen contained within the feed to produce additional moisture and carbon dioxide that is also adsorbed by the adsorption unit to produce the clean dry air product. In another aspect, the present invention relates to such a method and apparatus in which the clean dry air product is introduced into a cryogenic rectification process to produce one or more products of nitrogen or oxygen.
Clean dry air has many uses in the modem electronics industry. For instance, in production facilities, an atmospheric environment is required that is devoid of moisture and other impurities such as hydrocarbons, hydrogen and carbon monoxide that can detrimentally effect semiconductor production. When clean dry air is provided, filtering and drying units are used in combination with oil-free pumps. This apparatus is expensive and must be continually monitored.
Another use of clean dry air is in the production of ultra-high purity industrial gases that are in the main also used in semiconductor fabrication facilities. The clean dry air for such purposes is cooled to near dew point temperatures and then introduced into a cryogenic rectification column to produce the ultra-high purity industrial gas products such as nitrogen.
In any air separation process, it is necessary to remove impurities such as carbon dioxide and moisture from the feed air in that such impurities tend to freeze out during the low temperature process. The net effect of freezing out the impurities can be to cause stoppage of piping systems and conduits and to concentrate dangerous hydrocarbons. In ultra-high purity air separation processes adsorption systems are used in which the feed air is prepurified by adsorption units that are also designed to remove carbon monoxide and hydrogen. A stream lean in heavy impurities is produced and remaining light impurities are stripped from such stream to produce a product.
It is to be noted that hydrocarbons exist in the air in trace amounts. However, when oil lubricated machinery, such as air compressors, are used in connection with air separation, oil vapor is produced that acts as a source of hydrocarbons introduced into the feed air. Such a level of hydrocarbons would be unacceptable in a clean dry air product or a compressed feed to an air separation plant designed to produce an ultra-high purity product. Therefore, when clean dry air is required, expensive oil-free compressors are used.
As will be discussed, the present invention provides a method and apparatus for manufacturing clean dry air that can use conventional adsorbent beds and also, conventional compressors to produce a clean dry air product that contains no more than 100 parts per billion each of hydrocarbons and moisture. Furthermore, the methodology and apparatus at the present invention have particular application to prepurification units used in air separation plants to allow for production of ultra-high purity industrial gas products.